I figured this out finally... first, if your familiar with XML, you can just edit the xml file.
But even easier... I did this in Windows 7, not sure if XP is the same... to edit your water profile, just go to where your beersmith data is stored. For me, it was under 'My Documents' in a BeerSmith2 folder. Once you are in this folder, scroll down until you see the file called 'Water'. Right mouse click and click 'Edit BeerSmith 2 File'. Beer Smith comes up and you see all your water profiles. Just double click the entry you want to update, make your changes and click Okay. It's that easy.
John